Vehicle air conditioning systems are well known in the art. Such systems conventionally include an air duct, which is selectively connected to the external air or to the interior of the vehicle cabin, a fan for causing the air to flow, and an evaporator unit within the duct for cooling the air. The cold air output from the evaporator unit may be supplied directly to various outlets within the vehicle cabin or some of the cold air may be passed through a heating heat exchanger whose heated air output is mixed with the cold air to provide temperature control of the air output to the cabin. Diversion of the cold air through the heat exchanger is controlled by a so-called “blend door”, which in one extreme position causes all of the cold air to flow through the heat exchanger and in the opposite extreme position causes none of the air to flow through the heat exchanger. In intermediate positions different proportions of cold air and heated air can be provided.
As will be seen in FIG. 1, the cold airflow 22 is concentrated on one side of the air duct and the hot air 21 to the other side.
In modern vehicles, there are a number of air outlets into the vehicle cabin and these outlets are connected to the air duct by a corresponding number of output ducts. Two such ducts are shown in FIG. 1. As will be seen with reference to FIG. 1, a first upper duct 41 is disposed on the side of the system which will tend to provide cold air and the second lower duct 42 is disposed on the side of the system which will tend to provide hot air. When the temperature of the upper duct 41 and lower duct 42 are different, this is known as bi-level stratification.
It is desirable to be able to provide air outlets which are all at substantially similar temperatures. This may not be possible in the prior art arrangements due to the above-mentioned spatial distribution of air temperature within the air conditioning system.
Attempts have been made to provide improved mixing of hot and cold air at the output of an air conditioning system; however, these attempts have caused unacceptable temperature stratification and pressure drops, as well as substantial increases in manufacturing costs due to complex parts and assemblies.